1. Field of the Invention
This invention relates to a thermoplastic resin-silicone rubber composite shaped article comprising a layer of a thermoplastic resin and a cured layer of an addition polymerization type silicone rubber composition in the form of a laminate of these layers. The present invention is to provide new and useful medical devices made from the above composite shaped article, such as blood bag, medical tube and the like.
2. Description of the Prior Art
In general, silicone rubbers are superior in thrombus resistance and histocompatibility and have been expected as a medical material. However, they are used only in a limited amount in medical field because of their high cost and low mechanical strength.
Of thermoplastic resins being used in medical applications, soft vinyl chloride resins, by the addition of a plasticizer, a high molecular elastomer or the like, have flexibility, excel in transparency, and are good in adhesion and processability by high frequency or other method. However, the soft vinyl chloride resins have a hygienic problem of dissolution of plasticizer and the like into an adjacent liquid and, moreover, are inferior in thrombus resistance, histocompatibility, etc.
Olefin resins, particularly, polyethylene, polypropylene and ethylene-propylene copolymers are inexpensive and are superior in toughness and rigidity. However, they are insufficient in flexibility and thrombus resistance.
Urethane resins excel in toughness and flexibility; however most of them are low in rigidity and all urethane resins except segmented ones are insufficient in thrombus resistance.
Styrene resins excel in transparency and rigidity and are widely used in medical utencils, food packaging, etc. However, they are insufficient in flexibility and poor in thrombus resistance.
Thus, silicone rubbers and various thermoplastic resins now in use in medical applications each have strong points and weak points. Therefore, various attempts have been made of using two or more of these materials as one composite material.
Conventional silicone rubbers and resins are generally inactive and poor in adhesivity. Their adhesion to other resins is not sufficient even if they contain polar group-containing components present in condensation type RTV silicone rubbers or in so-called self-adhering silicone rubbers disclosed in Japanese Patent Application Kokai (Laid-Open) No. 24258/77, etc.
With respect to vinyl chloride resins, particularly, soft vinyl chloride resins, it has been generally thought that their strong adhesion to silicone rubber is difficult due to the effect of additives contained in the vinyl chloride resins such as a stabilizer, a plasticizer and the like. In order to overcome this drawback, there were proposed various methods in which the surface of a soft vinyl chloride resin is treated, for example, with a primer and then a silicone rubber layer is formed thereon. However, these methods had drawbacks in that (a) the process are complex, (b) many primers use a solvent such as ethyl acetate, toluene or the like and the solvent may remain partly and (c) the adhesion between the vinyl chloride resin and the silicone rubber layer causes separation with the lapse of time.
Japanese Patent Application Kokai (Laid-Open) No. 156083/79, etc. proposed a method wherein the surface of a vinyl chloride resin is subjected to low temperature plasma treatment and then thereon is formed a cured layer of a condensation type RTV silicone rubber. Japanese Patent Application Kokai (Laid-Open) No. 32773/83 proposed the modification of a vinyl chloride resin material in which the surface of the vinyl chloride resin material is subjected to plasma treatment or the like to form a cured layer and then thereon is formed a silicone resin layer composed of a dimethylpolysiloxane or an alkyl group-modified dimethylpolysiloxane. From these methods, it is clear that a silicone resin can be allowed to adhere to the surface of a vinyl chloride resin. However, it is difficult to subject the inner surface of a small diameter tube or a long tube made of a vinyl chloride resin material to a complete low temperature plasma treatment to form a cured layer.
Olefin resins are crystalline resins of no polarity and are hardly soluble in solvents. Therefore, their adhesion to metals or plastics is very difficult. Their strong adhesion particularly to silicone rubbers have been thought to be almost impossible.
Hence, in order to obtain adhesion between an olefin resin and a silicone rubber, there were made various attempts in which (1) the surfaces of the olefin resin and the silicone rubber are each subjected to a physical treatment such as corona discharge or the like or to a chemical treatment by a bichromic acid-sulfuric acid mixture or the like to cause surface oxidation and form an oxide film containing polar groups such as carbonyl group and the like and then (2) these two treated surfaces are allowed to adhere to each other by the use of an adhesive of epoxy-polyamide, nitrile rubber, isocyanate, cyanoacrylate or other type. In any of these attempts, however, no practically usable adhesion could be achieved.
Methods for adhesion between various base materials and silicone rubbers via various primers are described in Japanese Patent Application Kokai (Laid-Open) No. 23667/82, Japanese Patent Application Kokai (Laid-Open) No. 162711/82, etc. However, no reporting has been made yet regarding strong adhesion between thermoplastic resins such as urethane resins and styrene resins and addition polymerization type silicone rubbers without requiring the above primer treatment which is complicated.
Thus, use of composite materials between thermoplastic resins and silicone rubbers have been strongly desired; however no such materials which can be put into practical applications have been available.
With respect to soft vinyl chloride resins which contain a plasticizer, etc., dissolution of the plasticizer, etc. into an adjacent liquid has been a concerned matter. However, no effective method for overcoming the problem has been established yet. For example, in Japanese Patent Application Kokai (Laid-Open) No. 116469/81, it is reported that plasticizer dissolution can be reduced by subjecting the surface of a soft vinyl chloride resin to low temperature plasma treatment. However, the plasma treatment is extremely difficult for shaped articles of long tube configuration particularly with a small inner diameter.
Also, it is said that plasma treatment deteriorates the biocompatibility of soft vinyl chloride resins. Therefore, the plasma treatment for soft vinyl chloride resins has not been put into practical application.